1. Field of the Invention
The present invention relates to an image pickup apparatus using a solid-state image sensor such as a CCD and, more particularly, to an image pickup apparatus provided with an improved arrangement for reducing moire.
2. Description of the Related Art
In a conventional type of image pickup apparatus using a solid-state image sensor, to suppress aliasing distortion (moire) which occurs when sampling is performed at the pitch of pixels of the image sensor, an optical low-pass filter is inserted between a photographic lens and the image sensor so that a signal component of frequency near a sampling frequency is attenuated.
However, the above-described conventional image pickup apparatus has a number of problems such as the following ones.
In general, such an optical low-pass filter is produced by utilizing the nature of double refraction of crystal plate or the like. Since a plurality of crystal plates are sometimes used in the state of being placed one upon another to obtain vertical, horizontal and oblique refraction, an increase in cost is incurred. Further, because of the thickness of the optical low-pass filter, it is necessary to lengthen the back focal distance of a lens.
Further, there is the great problem that the optical low-pass filter impairs a signal of frequency below a Nyquist frequency because it is in principle impossible to impart a sharp attenuation characteristic to the optical low-pass filter.